1. Technical Field
The present disclosure relates to a thin film transistor (TFT) for an electro-luminescence (EL) device and a method of fabricating the same.
2. Disclosure of Related Art
Display devices have many applications and act as an interface between electrical devices, such as computers and televisions, and a user. Display devices operate by changing information in the form of electrical signals into an image and providing the image to the user.
Display devices may be classified into an emissive display device, such as, for example, a cathode ray tube (CRT), a plasma display panel (PDP), a light emitting diode (LED), and an organic electro-luminescent display device (ELD), or a non-emissive display device, such as, for example, a liquid crystal display (LCD), an electrochemical display (ECD), and an electrophoretic image display (EPID).
CRT displays have been widely used for televisions or as a computer monitor because of their display quality and low cost. However, CRT image displays have disadvantages, such as, for example, flickering, heavy weight, large physical size, and high power consumption.
Flat panel display devices, such as LCDs, have rapidly grown in popularity due to their excellent display quality, low power consumption, small physical size, and light weight.
An electro-luminescence display device is another example of a flat panel display device. Electro-luminescence display devices are classified as organic electro-luminescence display devices or inorganic electro-luminescence display devices.
Inorganic electro-luminescence display devices apply a high electric field to a light emitting portion, thereby exciting the light emitting portion to emit light. To generate the light, the inorganic electro-luminescence display device needs a driving voltage from about 100 to about 200 volts.
Conventional organic electro-luminescence display devices include an organic electro-luminescent layer disposed between two electrodes. When an electron and a hole are injected into the electro-luminescent layer from the two electrodes, respectively, the organic electro-luminescence display device generates an exciton by coupling the electron to the hole, and generates light when the exciton is changed from an excitation state to a ground state. The organic electro-luminescence display device needs a driving voltage from about 5 to about 20 volts to generate the light. Organic electro-luminescence display devices have characteristics, such as, for example, a wide visual angle, a high response speed, and a high contrast.
Organic electro-luminescence display devices are applicable to active matrix type display devices and to passive matrix type display devices. The active matrix type electro-luminescence display device independently drives organic electro-luminescence display devices corresponding to pixels using a switching device such as a thin film transistor.
Conventional organic electro-luminescence display devices include a semiconductor layer (or a channel layer) or a lightly doped deposition (LDD) structure formed using a polysilicon having electrical properties superior to that of amorphous silicon.
When a semiconductor layer of a thin film transistor used in a conventional organic electro-luminescence display device is formed using polysilicon, or is formed in the LDD structure, the thin film transistor may have a complicated structure, the manufacturing time for the thin film transistor may be great, and a defect ratio of the thin film transistor may be high because of it's complicated structure.
Accordingly, an electro-luminescence display device using amorphous silicon and n+ amorphous silicon into which an n-type dopant is injected has been proposed.
However, when amorphous silicon and n+ amorphous silicon are used to form an electro-luminescence display device, the amorphous silicon may be partially etched back during patterning of the n+ amorphous silicon. As a result, the amount of current flowing through the amorphous silicon may be changed, thereby deteriorating the quality of the displayed image.
Also, when the n+ amorphous silicon is etched by an etch-back process, the etch uniformity of the n+ amorphous silicon may be deteriorated, thereby further diminishing display quality.